1. Field of the Invention
The present invention relates to a process for purifying lutein and zeaxanthin from crude marigold extracts that may contain high levels of chlorophyll pigments.
2. Description of the Related Art
The carotenoids comprise a group of natural pigments found abundantly in plants, some fish, crustaceans, birds, algae and bacteria. Within this group of pigments are the yellow carotenoids, including both the carotenes (e.g., .beta.-carotene) and xanthophylls (e.g., lutein and zeaxanthin), and the red carotenoids, including capsanthin, canthaxanthin and astaxanthin. These yellow and red carotenoids are often present in plants, especially flowering plants, together with other classes of pigments, including primarily green chlorophyll pigments.
Carotenoids and in particular, xanthophylls, from marigold extracts have been used for decades in the poultry industry for pigmentation of broiler skins and egg yolks. Lutein, is present at much higher concentrations than zeaxanthin in marigold extracts. Pigmenting formulations for use in the poultry industry having relatively high concentrations of zeaxanthin have recently appeared on the market, wherein the lutein has been isomerized to yield zeaxanthin (U.S. Pat. No. 5,523,494 to Torres and U.S. Pat. No. 5,973,211 to Rodriguez).
In addition to their commercial importance in the poultry industry, the carotenoids have recently received considerable attention from scientists with respect to their potential role in promoting human health. Compounds like .alpha. and .beta.-carotene, lutein and zeaxanthin have been shown to possess strong antioxidant activity, which may retard or prevent diseases like cancer, arteriosclerosis, cataracts, macular degeneration and others (Bowen, WO98/45241). Lutein and zeaxanthin are the only carotenoids present in the macular region of the human retina and are related to the normal function of the macula responsible for visual acuity. It has also been reported that carotenoids enhance the immune response. Free radicals produced as byproducts of metabolic processes and originating from environmental pollutants (such as nitrogen dioxide and ozone of polluted air, heavy metals, halogenated hydrocarbons, ionizing radiation and cigarette smoke) are implicated as causative factors in many of the above-mentioned diseases. Carotenoids are potent quenchers of the highly reactive oxygen free radicals that can initiate a cascade of detrimental chemical reactions. Carotenoids also function as chain-breaking antioxidants, especially at low partial pressures of oxygen. Thus, carotenoids can work to quench free radical-induced reactions and can also prevent generation of free radicals, thereby limiting free radical/oxidative damage.
Hand-picked marigold petals from Tagetes erecta contain one of the highest concentrations of carotenoids found in nature. Industrial scale culture of marigolds and mechanization of the harvesting process have increased the amount of harvested leaves, stems, weeds and other plant parts that are typically obtained along with the flower petals. Oleoresins with high levels of chlorophylls and related compounds are obtained when meals from such raw material are extracted. Consequently, the lutein and zeaxanthin concentrations are relatively lower in such oleoresins than in those obtained from hand picked flowers.
The marigold extracts with high chlorophyll content are normally saponified under alkaline conditions to complete hydrolysis of the carotenoids as well as the chlorophyll. Variable levels of other lipids, chlorophyllins and unsaponifiable matter are also normally present in the reaction mixture. Consequently, the relatively low concentration of xanthophylls in oleoresins from mechanically harvested marigold meals, as well as the variability in levels of contaminating pigments, have impeded the commercial development of xanthophyll products for human consumption. Thus, there remains a need for an industrial process for obtaining lutein and zeaxanthin concentrates of high purity from meals prepared from large-scale, mechanically-harvested marigold cultures, which may have high levels of chlorophyll.